An Improved Conditional Privacy Protection Scheme Based on Ring Signcryption for VANETs

Vehicular ad hoc networks (VANETs) can effectively provide vehicle driving safety, high-speed data communication, intelligent traffic management, and vehicle entertainment. However, compared with traditional networks, VANETs are more vulnerable to attacks from adversaries, such as eavesdropping, tampering, tracking users' privacy, etc. In order to provide security and privacy protection for VANET communication, many conditional privacy protection (CPP) authentication schemes have been reported. In 2021, Cai et al. designed a novel CPP scheme based on ring signcryption suitable for VANETs. They proved that their scheme enjoys confidentiality, unforgeability, anonymity of sender's identity, and traceability of malicious vehicle users. But we demonstrate their scheme has some defects in construction and security. First, there is a small flaw in the ring signcryption algorithm in the scheme, which makes a legitimate receiver unable to get the original message sent by the sender from the received valid ciphertext. Second, Cai et al.'s scheme cannot provide anonymous protection of an honest sender's identity. At the same time, it is unable to reveal the identity of a malicious vehicle user. Finally, we present an improved scheme of Cai et al.'s scheme and supply its security proofs in the random oracle model, and analyze its performance. Ours is superior to the original scheme in security and efficiency. It is very suitable for providing security and privacy protection for vehicular users in VANETs.